Nontypeable Haemophilus influenzae (NTHi) is a major causative agent for acute otitis media (middle ear infections) and respiratory infections. Acute otitis media and otitis media with effusion are common childhood diseases, second in frequency of occurrence only to the common cold (Stool et al., Pediatr. Infect. Dis. Suppl., 8:S11-S14, 1989). The annual cost of the medical and surgical treatment of otitis media in the United States is estimated at between three and four billion dollars (Berman, New Engl. J. Med., 332:1560-1565, 1995). Moreover, inappropriate antibiotic treatment of otitis media can lead to the emergence of multidrug-resistant bacterial strains. There is currently no vaccine available for prevention of NTHi infection.
Current efforts in developing an NTHi vaccine are focused on cell surface antigens such as outer membrane proteins and pili or fimbria (Kyd et al., Infect. Immun., 63:2931-2940, 1995; Deich et al., Vaccine Res., 2:31-39, 1995). Among these, the most promising is P6 protein which appears to be antigenically conserved and elicits the production of antibodies that are bactericidal in vitro. Lipooligosaccharide (LOS) is a major NTHi cell surface antigen. LOS contains both lipid A and oligosaccharide (OS) components. Because the lipid A component of LOS is toxic, it must be detoxified prior to conjugation to an immunogenic carrier.
Barenkamp et al. (Pediafr. Infect. Dis. J., 9:333-339, 1990) demonstrated that LOS stimulated the production of bactericidal antibodies directed against NTHi. McGehee et al. (Am. Journal Respir. Cell Biol., 1:201-210, 1989) showed that passive immunization of mice with monoclonal antibodies directed against LOS from NTHi enhanced the pulmonary clearance of NTHi.
Green et al. (Vaccines, 125-129, 1994) disclose an NTHi vaccine comprising a conjugate of NTHi OS and the mutant nontoxic diphtheria protein CRM.sub.197. The lipid A moiety was removed from LOS by treatment with acid, followed by derivatizing the resulting OS with adipic acid dihydrazide (ADH) and coupling to CRM.sub.197. Despite the showing of Barenkamp et al. that LOS stimulated production of bactericidal antibodies against NTHi, the conjugates of Green et al. were determined to be poorly imnmunogenic after injection into mice. Moreover, the conjugates did not elicit bactericidal antibodies against NTHi.
Thus, there is a need for a vaccine effective against NTHi. The present invention satisfies this need.